class Solution {
    public List<Integer> findSubstring(String s, String[] words) {
        List<Integer> res = new ArrayList<>();
        if (s == null || s.length() == 0 || words == null || words.length == 0)
            return res;
        int one_word = words[0].length();
        int word_num = words.length;
        HashMap<String, Integer> map = new HashMap<>(word_num);
        for (String word : words) {
            map.put(word, map.getOrDefault(word, 0) + 1);
        }
        HashMap<String, Integer> tmp_map = new HashMap<>(word_num);
        for (int i = 0; i < one_word; i++, tmp_map.clear()) {
            for (int j = i + one_word; j <= s.length(); j += one_word) {
                String word = s.substring(j - one_word, j);
                tmp_map.put(word, tmp_map.getOrDefault(word, 0) + 1);
                if (j / one_word > word_num - 1) {
                    int e0 = j - word_num * one_word;
                    String s0 = s.substring(e0, e0 + one_word);
                    if (map.equals(tmp_map)) res.add(e0);
                    tmp_map.put(s0, tmp_map.get(s0) - 1);
                    tmp_map.remove(s0, 0);
                }
            }
        }
        return res;
    }
}